Metallic sheath cable

ABSTRACT

A conductor cable includes a tubular metallic sheath for carrying one or more electrical conductors and/or one or more fiber optic elements and which, in various embodiments has a substantially rectangular transverse cross-sectional configuration defined by pairs of parallel sidewalls which enable selective bending of the cable generally about the major and minor axes of the sheath. The parallel sidewalls may have substantially transverse or angularly inclined corrugations formed along their lengths to facilitate bending of the cable in relatively small radius bends about the major and minor axes of the sheath.

This is a continuation-in-part from application Ser. No. 07/358,575,filed May 26, 1989, now U.S. Pat. No. 5,001,303.

BACKGROUND OF THE INVENTION

The present invention relates generally to metallic sheath cable, andmore particularly to a novel metallic sheath cable for carrying one ormore electrical conductors and/or fiber optic elements and having atubular metallic sheath of substantially rectangular transversecross-section configured to enable selective bending generally about themajor and minor axes of the sheath cross-section.

It is conventional to employ metal sheathed electrical cable in manytypes of electrical circuit systems. Traditionally, metal sheathed cablehas been classified in two basic categories; Type ALS (smooth andcorrugated aluminum and copper sheathed) and Type MC cable availablewith interlocked steel or aluminum tape. More recently, the NationalFire Protection Agency (NFPA) merged four basic cable types under theNational Electric Code as follows:

1. Smooth continuous aluminum sheath.

2. Continuous corrugated aluminum sheath.

3. Interlocked steel armor.

4. Interlocked aluminum armor.

These four types of metal sheathed cable have also been subjected torecognized industrial standards by industry certification groups such asUnderwriters' Laboratories, Inc., Northbrook, Illinois.

The selection of one or more of the aforelisted types of metal sheathedcable for a particular application is at least in part determined bytheir various characteristics. For example, applications requiringplenum and wet location installations generally require the use ofcontinuous impervious metal sheath, while portable equipment andfixtures generally call for the use of interlocked type steel sheath tofacilitate repeated flexing. Common to all metallic sheath cable typesis the need for a lightweight, readily strippable and easily pulledcable, with reliable grounding means and reasonable cost.

The more recent usage of fiber optic cables as an improved alternativeto electrical conductors for many applications has also brought aboutthe need for a metallic sheathed fiber optic cable which providesprotection to the fiber optic conductor elements and facilitatesinstallation of the fiber optic cable. The present invention addressesthese needs by providing a generally rectangular metallic sheathconstruction for electrical and/or fiber optic conductors which exhibitsthe advantages of prior metal sheath cable and provides significantimprovements in ease of installation, grounding safety, size, weight andeconomic savings.

SUMMARY OF THE INVENTION

One of the primary objects of the present invention is to provide anovel conductor cable having one or more electrical and/or fiber opticconductors carried within a tubular metallic sheath of substantiallyrectangular transverse cross-section and configured to enable selectivebending generally about the major and minor axes of the sheathcross-section.

A more particular object of the present invention is to provide a novelconductor cable for electrical and/or fiber optic conductors whichincludes a tubular metallic sheath having a substantially rectangulartransverse cross-sectional configuration defined by pairs of generallyparallel sidewalls having widths, respectively, substantially equal tothe major and minor axis dimensions of the sheath cross-section andwhich enable selective bending generally about the major and minor axesof the sheath.

Another object of the present invention is to provide a novel generallyflat conductor cable as described wherein selected ones of the parallelsidewalls have corrugations formed therealong to facilitate bendinggenerally about the major and minor axes of the sheath cross-section.

A feature of one embodiment of the electrical cable in accordance withthe invention lies in forming the corrugations in angularly inclinedrelation to a plane transverse to the longitudinal axis of the sheath,the corrugations on adjacent sidewalls either being offset or continuousin generally helical fashion.

Another feature of the electrical cable in accordance with the inventionlies in its ability to be selectively bent generally about the major andminor axes of the sheath rectangular cross-section in substantiallysmaller bending radii than heretofore obtainable under industrystandards on bend radius.

Further objects, advantages and features of the invention will becomeapparent from the following detailed description of various embodimentsof the invention when taken in conjunction with the accompanyingdrawings wherein like reference numerals designate like elementsthroughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view of a metallic sheath conductorcable constructed in accordance with one embodiment of the presentinvention;

FIG. 2 is a fragmentary plan view of a metallic sheath conductor cablesimilar to FIG. 1 but having the sidewall corrugations angularlyinclined relative to a plane transverse to the longitudinal axis of thecable;

FIG. 3 is a fragmentary side elevational view of an electrical cablesimilar to FIG. 2 but having the sidewall corrugations formed so as toestablish a continuous generally helical corrugation pattern along thelength of the cable sheath; and

FIGS. 4-7 are fragmentary perspective views similar to FIG. 1 butillustrating various alternative embodiments of a metallic sheathconductor cable constructed in accordance with the invention.

DETAILED DESCRIPTION

Referring now to the drawings, and in particular to FIG. 1, a conductorcable constructed in accordance with one embodiment of the invention isindicated generally at 10. The conductor cable 10, which may be termed aor metallic sheath cable, includes an elongated tubular metallic sheath12 of generally rectangular transverse cross-sectional configurationhaving major and minor axes. The sheath 12 is preferably made ofaluminum or an aluminum alloy and has a first pair of parallel generallyflat sidewalls 12a and 12b of a width generally equal to the major axisdimension of the sheath rectangular cross-section. In the embodimentillustrated in FIG. 1, the sidewalls 12a and 12b have their respectivelongitudinal marginal edges formed integral with correspondinglongitudinal marginal edges of a second pair of parallel generally flatsidewalls 12c and 12d which are normal to the walls 12a and 12b and areof a width generally equal to the minor axis dimension of the sheath.

The sheath 12 may have a nominal wall thickness of approximately 0.022inch and may be formed as a seamless continuous sheath or alternativelyformed from a flat strip of metal sheet which is formed into a generallyrectangular tubular sheath and has its abutting longitudinal edgeswelded to form a closed liquid impervious sheath. The sheath 12 couldalso be formed from a flat metallic armor strip which is helicallywrapped about a mandrel or the like to form a generally rectangularsheath, the abutting or juxtaposed edges of the helically wound stripbeing preferably interlocked as by forming the marginal edges of thestrip into generally sine wave configuration and overlapping theadjacent edges in nested interfitting relation.

In accordance with one feature of the conductor cable 10, the sheath 12is configured to enable selective bending through relatively smallradius bends generally about the major and minor axes of the sheathtransverse cross-sectional configuration. In the embodiment illustratedin FIG. 1, the first and second pairs of sidewalls 12a, 12b and 12c, 12dhave generally transverse corrugations formed along their longitudinallengths. For example, the parallel sidewalls 12a and 12b have identicalgenerally transverse corrugations 16 formed therein which are inparallel equal spaced relation, with each corrugation lying in a planesubstantially transverse to the longitudinal axis of the sheath 12.Similarly, the sidewalls 12c and 12d each have parallel and equallyspaced transverse corrugations 20 formed along their longitudinallengths so that each corrugation lies in a plane substantiallytransverse to the longitudinal axis of the sheath. The corrugations 16and 20 may be formed as generally narrow flat deformations in thesidewalls or as smooth arcuate concave channels. Corrugations 16 areoffset longitudinally from the corrugations 20 so that the corrugationsformed in the sidewalls 12a,b do not intersect the corrugations in thesidewalls 12c,d.

The rectangular metallic sheath 12 is sized to receive at least one, andpreferably at least two, insulated electrical conductors, one of whichis indicated at 24. Alternatively, the metallic sheath 12 may carry oneor more fiber optic elements or conductors, one of which is indicated at25 in FIG. 1. The sheath 12 of conductor cable 10 may also carry acombination of electrical and fiber optic conductors such as theelectrical conductor 24 and fiber optic conductor 25 illustrated inFIG. 1. The electrical conductor 24 may comprise, for example, a No. 12AWG solid electrical conductor having a conventional coaxial insulationlayer or jacket 26. The fiber optic conductor 25 is of conventionaldesign and includes an optic fiber element 25a having a coaxialinsulation or buffer layer 25b and a coaxial outer braided cover layer25c. For purposes of description, the fiber optic conductor 25 may inits entirety be termed a fiber optic cable or fiber optic element.

The electrical and fiber optic conductors 24 and 25, or a pair of eitherelectrical conductors 24 or fiber optic conductors 25, extendlongitudinally within the metallic sheath such that the longitudinalaxes of the conductors are coplanar and parallel to the longitudinalaxis of the sheath. The insulated conductors are preferably maintainedin juxtaposed relation by conventional bedding tape 28 which may behelically wound or folded along the longitudinal length of the pairedconductors. Alternatively, the insulated conductors 24 and 25 may bemaintained in parallel relation by an extruded jacket covering or thelike. The sheath 12 is configured to provide a suitable strippingclearance between the internal wall surfaces of the metallic sheath andthe external surface of the bedding tape 28. In a two-conductor No. 12AWG electrical cable, it has been found that a minor axis outerdimension of approximately 0.192 inch and a major axis outer dimensionof approximately 0.302 inch enables the rectangular sheath 12 to be bentin relatively small radius bends about either the major or minortransverse axes.

FIG. 2 illustrates an alternative embodiment of a conductor cable,indicated generally at 30, which may also be termed a metallic sheathcable and which includes a metallic sheath 32 of generally rectangulartransverse cross-sectional configuration similar to the cross-sectionalconfiguration of the metallic sheath 12. The sheath 32 thus has a majortransverse axis of greater dimension than the minor transverse axisdimension. The electrical cable 30 also carries a pair of insulatedconductors in the form of an electrical conductor 24 and a fiber opticelement or conductor 25, or alternatively a pair of electricalconductors or pair of fiber optic elements, which are preferably coveredwith a suitable jacket or bedding tape 28 and have coplanar longitudinalaxes parallel to the longitudinal axis of the sheath.

In the embodiment of FIG. 2, the sheath 32 has a first pair ofsubstantially parallel sidewalls 32a and 32b of a transverse widthsubstantially equal to the major transverse dimension of the sheath. Thelongitudinal marginal edges of sidewalls 32a,b are formed integral withcorresponding edges of a second pair of parallel sidewalls 32c and 32dwhich lie in planes normal to the sidewalls 32a, 32b and are of atransverse width substantially equal to the minor axis dimension of therectangular sheath. The cable 30 differs from cable 10 in that thesidewalls 32a and 32b have parallel spaced corrugations 34a and 34b,respectively, which are similar to the corrugations 16 but are angularlyinclined relative to a plane transverse to the longitudinal axis of thecable. In the embodiment of FIG. 2, the centerline of each concavecorrugation 34a,b forms an included angle of approximately 15° with aplane transverse to the longitudinal axis of the sheath 32, asconsidered in the plan view of FIG. 2. The sidewalls 32c and 32d alsohave parallel spaced corrugations formed therein, as indicated at 36aand 36b, which are similarly angularly inclined at approximately 15° toa plane transverse to the longitudinal axis of the metal sheath asconsidered in the planes of sidewalls 32c,d. The angled or inclinedcorrugations 34a,b in the sidewalls 32a,b are offset from thecorrugations 36a,b in the sidewalls 32c,d so that the corrugations donot intersect each other. In other respects, the cable 30 may have thesame dimensional size and stripping clearances as cable 10 so as toenable relatively small radius bending about the major and minortransverse axes of the sheath.

FIG. 3 illustrates a side elevation of another embodiment of a conductorcable, indicated generally at 40, which also may be termed a metallicsheath cable and which includes a metallic sheath 42 of generallyrectangular transverse cross-sectional configuration similar to thecross-sectional configurations of the aforedescribed metallic sheaths 12and 32. The rectangular sheath 42 has a first pair of parallel generallyflat sidewalls 42a and 42b of a transverse width substantially equal tothe major transverse dimension of the sheath, and has a second pair ofparallel generally flat sidewalls 42c and 42d formed integral with andnormal to the sidewalls 42a,b. The sheath 42 carries a pair of insulatedconductors, such as a pair of electric conductors, a pair of insulatedfiber optic elements, or an electrical conductor and a fiber opticelement, which are maintained in parallel coplanar relation by a beddingtape wrap 28 such that the longitudinal axes of the conductors areparallel to the longitudinal axis of the metallic sheath.

The sidewalls 42a,b and 42c,d of the metallic sheath 42 each haveparallel spaced corrugations, indicated at 44a,b and 46a,b,respectively, formed along their longitudinal lengths. The corrugations44a,b and 46a,b are inclined or angled relative to a plane transverse tothe longitudinal axis of the sheath at angles of inclination ofapproximately 15°, as considered in the planes of the respectivesidewalls, similar to the corrugations 34a,b and 36a,b in sheath 32. Themetallic sheath 42 differs from sheath 32 in that the corrugations 44a,band 46a,b intersect each other so as to form a generally helicalcorrugation along the length of the sheath 42. In other respects, thecable 40 has similar dimensional size and stripping clearances as theaforedescribed conductors cables 10 and 30 and enables relatively smallradius bending about the major and minor transverse axes of the sheath42.

In the embodiments of FIGS. 1, 2 and 3, the corrugations in thecorresponding rectangular sheath sidewalls may be formed so as toestablish approximately 4.5-5 corrugations per linear inch along thelongitudinal lengths of the sheaths. A bare or insulated ground wire mayalso be carried with the conductors 24a,b within the bedding tape wrapif desired. Each corrugated sheath may have a profile thickness ofapproximately 0.065-0.080 inch with a corrugation depth of betweenapproximately 0.040 and 0.055 inch.

FIG. 4 illustrates another embodiment of a conductor cable, indicatedgenerally at 50, which may also be termed a metallic sheath cable. Theconductor cable 50 includes a metallic sheath 52 of generallyrectangular transverse cross-sectional configuration adapted to carry apair of insulated electrical conductors 24 or a pair of fiber opticelements 25, or an electrical conductor and a fiber optic element, whichare preferably covered with a suitable jacket or bedding tape 28 suchthat the longitudinal axes of the conductors are coplanar and parallelto the longitudinal axis of the sheath 52. The metallic sheath 52 hasfirst and second pairs of generally flat parallel sidewalls 52a,b and52c,d which are interconnected along their marginal longitudinal edgesthrough rounded or arced corner edge surfaces indicated at 54a-d. Thesidewalls 52a,b and 52c,d have parallel generally equidistantly spacedtransverse corrugations formed along their longitudinal lengths, such asindicated at 56a,b and 58a,b, in similar fashion to the corrugations inthe sidewalls of the metallic sheath 12. The respective corrugations56a,b and 58a,b terminate at the rounded corner edges 54a-d and areoffset relative to each other so that the corrugations in the sidewalls52a,b do not intersect the corrugations in the sidewalls 52c,d. In otherrespects the electrical cable 50 may have similar dimensional size andstripping clearances as the cable 10 and is bendable in relatively smallradius bends about the major and minor transverse axes of the sheath.

FIG. 5 illustrates another embodiment of a conductor cable, indicatedgenerally at 60, which also may be termed a metallic sheath cable andwhich includes a metallic sheath 62 of substantially rectangulartransverse cross-sectional configuration similar in dimensional size tothe sheath 12 of the conductor cable 10. The metallic sheath 62 hasfirst and second pairs of generally flat substantially parallelsidewalls 62a,b and 62c,d, respectively, which have their longitudinalmarginal edges integrally connected so as to form the generally flatrectangular sheath. The sheath 62 may also carry a pair of insulatedelectrical conductors 24 or fiber optic elements 25 which are preferablycovered with a suitable jacket or bedding tape 28 such that thelongitudinal axes of the conductors are coplanar and parallel to thelongitudinal axis of the sheath. The sheath 62 differs from theaforedescribed sheath 12 in that the sidewalls 62a and 62b, which definethe major axis sidewalls of the sheath, do not have corrugations formedtherein but are generally smooth flat surfaces. The sidewalls 62c,d haveparallel spaced transverse corrugations 64a and 64b, respectively,formed along their longitudinal lengths. The major and minor transverseaxes of the sheath 62 are established to enable selective bending of thecable 60 through relatively small radius bends generally about the majorand minor transverse axes of the sheath.

FIGS. 6 and 7 illustrate further embodiments of a conductor cable inaccordance with the invention, indicated at 70 and 80, respectively,each of which may alternatively be termed a metallic sheath cable offlat construction configured to enable selective bending throughrelatively small radius bends generally about major and minor transverseaxes of the respective cables. More particularly, the electrical cable70 includes a tubular metallic sheath 72 having generally flat buttransversely corrugated parallel sidewalls 72a and 72b which lieparallel to the major transverse axis of the sheath. The sheath 72 alsohas a second pair of generally flat but transversely corrugated parallelsidewalls 72c and 72d which lie in planes normal to the planes of thesidewalls 72a,b and which are interconnected to corresponding edges ofthe sidewalls 72a,b through curved or arced corner walls 74a-d. In theembodiment of FIG. 6, transverse corrugations 76a and 76b are formed inthe sidewalls 72a and 72b, respectively, and lie in generally transverseplanes which also contain the center axes of a corresponding pair oftransverse corrugations 76c and 76d formed in the sidewalls 72c and 72d,respectively. The respective transverse corrugations 76a,b and 76c,d donot extend into the curved corner walls 74a-d and thus do not formcontinuous corrugations about the periphery of the sheath.

The electrical cable 80 includes a rectangular metallic sheath 82 havinggenerally flat parallel sidewalls 82a and 82b which lie in planesparallel to the major transverse axis of the sheath. The sidewalls 82a,bare interconnected through generally semi-circular sidewalls 84a and 84bso as to form a smooth tubular metallic sheath having an oval transversecross-sectional configuration which is defined broadly as generallyrectangular. Both of the electrical cables 70 and 80 may carry a pair ofcovered parallel insulated electrical conductors, a pair of fiber opticconductor elements, or a combination of electrical and fiber opticconductors, and are sized to enable relatively small radius bendingabout their major and minor transverse axes. The various embodiments ofthe conductor cables in accordance with the invention exhibit a numberof advantages over prior smooth wall and corrugated cable of generallycircular transverse cross-section. For example, the flat generallyrectangular conductor cables of the present invention may carry parallelindividual circuit and grounding conductors which results in savingapproximately 3% conductor length over the use of conventional cabledelectrical conductors as employed in prior metallic sheath cables ofcircular transverse cross section. The parallel circuit and groundingconductors within the metallic sheaths result in less conductorresistance per unit length of cable over twisted conductors and alsosave the installer time by not having to untwist the conductors whenterminating.

The generally flat metallic sheath conductor cables of the inventionalso optimize space saving in installations, as well as providingaesthetic improvements, by enabling the exposed sheath to be laid flatalong walls, floor moldings, ceiling coves, and door frames and the likethrough the ability to bend the sheath in small radius bends about boththe major and minor transverse axe of the cables.

Existing electrical codes place restrictions on bend radius forconventional electrical cables of circular cross-section. For example, abend radius of at least seven times the cable diameter must generally bemaintained for a corrugated metal clad electrical cable of circularcross-section, and a minimum bend radius of ten times the cable outerdiameter must be maintained for smooth wall metal clad cable of circularcross-section. The various embodiments of conductor cable in accordancewith the present invention can be readily bent about either their majoror minor axes in smaller radii than allowed under existing codes forsimilar AWG size cable but of circular cross section. The conductorcable of the present invention may be bent about its minor axisapproximately one-half the bend radius required for prior electricalcables of the same AWG size having circular cross-section. This isparticularly advantageous in installing and terminating electrical cableat junction boxes where space may be limited and where angle, offset andright-angle bends in the cable are necessary. A further advantage of theflat rectangular conductor cable of the present invention is that whenemployed as an electrical cable it enables a relatively large flatsurface area of the cable to be clamped by a connector fixed to aterminal end of the cable, thereby substantially lowering the electricalgrounding path resistance and preventing rotation of the electricalcable relative to the connector. Such improved electrical groundingsignificantly reduces the likelihood of poor grounding terminationswhich can lead to unsafe grounding hazards.

While preferred embodiments of the invention have been illustrated anddescribed, it will be understood that changes and modifications may bemade therein without departing from the invention in its broaderaspects. Various features of the invention are defined in the followingclaims.

What is claimed is:
 1. An electrical conductor cable comprising anelongated tubular metallic sheath of generally rectangular transversecross-sectional configuration having a greater major axis dimension thanminor axis dimension, and at least one insulated electrical conductorextending longitudinally within said sheath and having a substantiallycircular transverse cross-sectional configuration, said sheath beingdefined by first and second pairs of substantially parallel mutuallyperpendicular sidewalls having respective widths substantially equal tosaid major and minor axis dimensions and connected along longitudinalmarginal edges so as to form an uninterrupted closed internal passage toreceive said electrical conductor, said sheath having a substantiallyseamless wall of uniform thickness about its full periphery, said firstpair of sidewalls being generally flat sidewalls, and said second pairof sidewalls being convexly curved sidewalls connected alonglongitudinal marginal edges to corresponding longitudinal marginal edgesof said first pair of sidewalls, said sheath and electrical conductorenabling bending of said cable about said major and minor axes of saidsheath.
 2. A conductor cable comprising an elongated tubular metallicsheath of generally rectangular transverse cross-sectional configurationhaving a greater major axis dimension than minor axis dimension, and atleast one conductor element extending longitudinally within said sheath,said sheath being defined by first and second pairs of substantiallyparallel, continuous and mutually perpendicular sidewalls connectedalong longitudinal marginal edges so as to form an uninterrupted closedinternal passage to receive said conductor element, said sheath being ofuniform wall thickness about its full periphery, and said sidewallsbeing corrugated along their longitudinal lengths to enable selectivebending of the cable about said major and minor axes.
 3. A conductorcable as defined in claim 2 Wherein said conductor element comprises afiber optic element.
 4. A conductor cable as defined in claim 3including an electrical conductor extending longitudinally within saidsheath.
 5. A conductor cable as defined in claim 4 wherein said fiberoptic element and electrical conductor have insulating layers coaxiallytherealong, and including means securing said electrical conductor andfiber optic element in substantially parallel relation extendinglongitudinally within said sheath.
 6. A conductor cable as defined inclaim 2 wherein said corrugations are disposed generally transverse tothe longitudinal axis of said metallic sheath.
 7. A conductor cable asdefined in claim 3 wherein said first pair of sidewalls are generallyflat, and said second pair of sidewalls are convexly curved andconnected along longitudinal marginal edges to longitudinal marginaledges of said first pair of sidewalls so as to establish a sheath havinga generally oval transverse cross-sectional configuration.
 8. Aconductor cable as defined in claim 3 wherein said fiber optic elementincludes an external braided layer disposed coaxially along the lengthof said fiber optic element.
 9. A conductor cable as defined in claim 8including an insulated electrical conductor element disposed within saidtubular sheath and extending longitudinally therein.